Over the past few years, there has been dramatic growth in the adoption of the mobile cellular telephone to the extent that it can largely be considered ubiquitous. This has led to a dichotomy in the world of enterprise voice call routing—for many years the voice world was neatly divided into “home” and “work” numbers. With mobile phones, the lines between a personal and an office extension are blurred—users want the flexibility of the mobile phone but the rich feature set of the modern desk phone. There is a need to reconcile this situation by allowing users to select what functionality they wish to receive when away from the desk.
There have been various schemes to provide enterprise telephony on mobile handsets. These schemes can be broken down into those that are a mobile handset as an extension of an office line and those that are a mobile handset as a replacement of an office line. The goal of the mobile handset as an extension of an office line model is to “extend” the office extension to the phone. An example is the Avaya “Extension to Cellular” system. This system binds together a mobile phone number to an office extension and when the PBX receives an inbound call to the office extension it also rings the mobile phone number bound to it by the enterprise communications server (ECS). Whichever phone picks up first is considered to “own” the call. In this way, users can give out just their office phone number, but can receive calls placed to that number on their cellular phones.
In order to provide additional functionality (such as being able to place outbound calls using the office extension but from the mobile phone), products such as Feature Name Extensions (FNE) exist. These expose internal PBX functionality through externally dialable phone numbers. For example, if a remote user wants to place an outgoing call from their office extension, they would first dial into the FNE number from their mobile phone. The PBX would recognize the user by cross referencing the mobile phone number through caller id, and request that the user enter a PIN. Once this has been done, the PBX allows the user to dial a number and completes the call on the user's behalf.
The mobile handset as a replacement of office line model focuses on providing an implementation of software on a mobile handset such that it can communicate directly with the enterprise PBX and effectively “become” an office phone. Examples of this are the Avaya IP softphone (which runs on PCs and Windows Mobile pocket pcs) and the Research In Motion 77xx series of BlackBerry® devices. While this model may provide robust and flexible functionality, the issue becomes one of transport of data. Because the device needs to be able to communicate directly with the PBX, it requires a secure channel over which to communicate—typically over a virtual private network (VPN). As bulk voice data is transported over the same channel, this requires a broadband connection for mobility—something that cannot be supported on generic wireless networks. For example, the RIM 77xx Blackberry® device requires a Wifi connection in order to provide enterprise voice functionality (over the session initiation protocol (SIP)). This bandwidth requirement makes the pure-replacement model one of limited use.